1. Technical Field
The present invention relates to an engine for a working machine, more specifically to an engine that can be used in a portable working machine, such as a brush cutter, a chain saw, and a power blower.
2. Related Art
Conventionally, this sort of engine for a portable working machine includes a casing to cover the engine and a cooling fan coupled to a crankshaft. The engine is cooled by flowing cooling air between the engine and the casing.
The engine for a portable working machine is used in such as a brush cutter, a chain saw and a power blower. Being held up by the user, the engine is tilted in different directions in use. At work, sometimes a portable working machine is placed on the ground while its engine is in the idle state. For example, an engine for a portable working machine has been known that has a fuel tank and a bottom cover in its lower part in order to prevent foreign matters such as weeds from getting into between the engine and the casing when the portable working machine is placed on the ground (see Japanese Patent Application Laid-Open No. 2008-75558).
The above-described engine for a portable working machine has a problem that the fuel tank and the bottom cover provided in its lower part may prevent a sufficient amount of cooling air from flowing in the engine. This may cause the performance of the engine to degrade. Therefore, the engine for a portable working machine is designed to ensure that a sufficient amount of cooling air flows therein by forming air flow ports in the bottom cover. However, if the air flow ports of the bottom cover are widened, it is possible to increase an amount of cooling air flowing in the engine for a portable working machine, but foreign matters easily come in the engine.